Mn, Fe, Cu and Zn were determined in topsoil and herbage samples from sites in North West Pembrokeshire. Means and ranges for these elements are given and the distribution is shown throughout the sampled area.

There are no clear relationships between the total amounts of these elements in the soils and the amounts found in herbage but it is shown that soil drainage strongly influences both soil and plant concentrations, and pH has a strong influence on Mn concentrations in soils and plants.

Seasonal variation in plant uptake of these elements is discussed and the effect of soil contamination of herbage, especially on Fe content. It is hoped that data from this area can be used as a guide to the range of values found for Mn, Fe, Cu and Zn in soils and herbage of an area relatively unpolluted from industrial sources for comparison with more polluted regions.

Regression models were constructed to predict the yields and digestibilities of herbage cut in different sequences of harvests.

The yield model used a seasonal production curve modified by the effects of defoliation. Values for the model parameters were obtained by fitting the model to experimental data using a non-linear regression procedure. When these parameters were used, to predict treatment effects in another series of experimental data, good agreement was obtained. The digestibility model incorporated the effect on digestibility time of year, regrowth time and yield.

Using the models to interpolate between the results of cutting experiments, annual yields were shown to increase with the date of first cut and also with the interval between subsequent cuts, whereas the average digestibility of the harvested material ecreased with the date of first cut and with the subsequent cutting interval. Finally, a procedure was devised for combining the two models in order to find an optimum cutting strategy for a hypothetical animal production system.

In two experiments with female Scottish Blackface or Border Leicester x Scottish Blackface sheep nine or ten animals were slaughtered in mid lactation and the remainder either in November at the time of the subsequent mating (Expt 1) or at weaning (Expt 2).

The sheep were infused periodically, including just before slaughter, with 100 μCi tritiated water (TOH) in order to measure total body water by dilution and to estimate body fat using the inverse relationship between the proportions of fat and water in the body. The accuracy of the methods was assessed when the sheep were slaughtered. In the ton lactating Scottish Blackface sheep of Expt 1 fat made up 11.5% of the total body weight with an S.D. of 8·38% whereas the 11 sheep slaughtered at mating were twice as fat (23·2, S.D. 4·01 %). The 25 Border Leicester × Blackface sheep were all thin, whether they were slaughtered in mid lactation (4·4, S.D. 2·56%) or at weaning (3·4, S.D. 2·81%).

The standard error of estimate of body water from TOH space in Expt 2 was 1·2 kg c.v. 2·8%) and lower in Expt 1.

The precision with which an animal could be weighed was very important in determining the accuracy with which body fat could be predicted from live weight and TOH space. In both experiments the standard error of estimate for body fat in lactating sheep was between 600 and 700 g, compared with 1·3–2·7 kg when body fat was predicted from live weight alone. These estimates were sufficiently accurate to be of value in following changes in body composition in live animals as their nutritional and physiological state alters and for comparing animals in groups where the average fatness is greater and the range wider than in the sheep used in Expt 2.

The results of 83 experiments with nine levels of nitrogen and six experiments with seven levels were used to investigate models of the response of spring barley to nitrogen. Of the eight models tested, the inverse quadratic, Greenwood's modification of the inverse linear and two intersecting straight lines represented the yield/fertilizer relationship well, although no one model fitted best at every site.

The three models differed little in their average predicted optimal yields, but a slightly smaller average optimal dressing was predicted from two straight lines.

The potential offered for plant breeding programmes by visual scoring techniques for plant water status was investigated in rice and spring wheat. It was found that differing plant morphology could seriously bias visual estimates of leaf water potential, particularly in spring wheat. In spite of this problem, it was found that at least for rice, this type of approach may have potential in future breeding programmes where an estimate of leaf water status is required, such as those for drought tolerance, so long as a high intensity of selection is not necessary.

A general equation for predicting the movement of interacting and non-interacting solutes is proposed. Equations to predict the leaching fractions and mean displacement depth of linearly adsorbed solutes have been derived from the solution of the general equation. A simple equation which considerably reduces the experimental and analytical work has also been derived to evaluate the adsorption coefficient. The predicted adsorption coefficient compares favourably with published data.

Perkins & Jinks's (1971) analysis was used to detect and measure the interactions between the environment and the additive, dominance and epistatic effects of the genes for final plant height, spike length, 100-grain weight and yield per plant in three barley (Hordeum vulgare) triple test crosses (DL 3 × IB 226, DL 3 × Jyoti and Jyoti × P 113) raised in two environments (normal irrigation and no irrigation). The j- and I- type epistasis was more sensitive to environmental differences than the i-type epistasis. Similarly, additive gene action responded more to the different environments than did the dominance action of the genes.

The concentrations of dry matter, crude protein, fat and ash and of Ca, P, Mg, Na and K were determined for 22 sets of twin foetuses, 33 of triplets and 11 of quadruplets of known gestational ages within the range 55–145 days. In addition, determinations were made of the concentrations of dry matter, crude protein, fat and ash in their associated placentae and empty uteri, and of dry matter, nitrogen, energy and ash in the foetal fluids. The dry matter, crude protein and fat concentrations in the placentae increased with foetal age and decreased with increasing litter size. Ash concentrations were unaltered. There was no effect of litter size or foetal age on the concentration of nutrients in the empty uteri. Dry matter and nitrogen concentrations in the fluids increased with foetal age but were independent of litter size, whereas ash concentrations increased with litter size but not with age.

The form of the mathematical model for foetal growth is considered in relation to the estimation of rates of accretion and the estimation of the differences in composition to be expected between foetuses that are heavy and others that are light relative to their age. When the weights of the foetal constituents were fitted by Gompertz equations extended to include foetal weight as an allometric term, the effects of litter size on foetal composition could be estimated from the foetal weights for each size of litter. Concentrations of dry matter and of most constituents in the foetuses became less as numbers of foetuses increased, irrespective of stage of gestation.

A description of the changing composition of the growing foetuses was provided by specific growth rates calculated from the fitted equations. With minor exceptions, derived estimates of foetal concentrations of each constituent were found to agree quite well with most previously published estimates for ovine foetuses, but similar agreement on daily accretion rates was not to be expected in view of the sensitivity of such estimates to the choice of model for foetal growth. Rates of accretion in the gravid uterus increased up to about 5 weeks before parturition and tended to level off thereafter, but most of them still increased slightly over the last 2 weeks, even in ewes bearing triplets or quadruplets. Taking account of the changes in the maternal body of the ewes, it was concluded that although the prolific ewes incurred a substantial energy deficit, and could not have consumed sufficient of the diet to avoid this, their intakes in late pregnancy were nevertheless adequate to support the high rates of accretion of protein and of minerals in the gravid uterus.

Normal and ketotio ewes pregnant with twin lambs were injected intramuscularly with 0·5 mg/kg body weight of trienbolone acetate. In the normal animals there was no significant change in the concentration of glucose, ketones, glycerol or NEFA in plasma.

Induction of ketosis by starvation produced a significant fall in the concentration of glucose in plasma and significant increases in the concentration of ketones, glycerol and NEFA. Trienbolone caused no further significant changes in the concentration of the four metabolites in the plasma of ketotio sheep.

Primed continuous simultaneous intravenous infusions of tracer amounts of [2-3H] and [U-14C]glucose were used to measure total entry rate and irreversible loss of glucose. Trienbolone caused significant decreases in both these measurements in normal pregnant sheep. Production of ketosis by starvation had the same effect. Trienbolone produced no significant additional effect in the ketotic sheep and no alleviation of the clinical signs of the hyperglycaemic ketosis.

These results are discussed in relation to the assessment of the potential value of trienbolone as a treatment of pregnancy toxaemia of sheep.

The relation between the ratio of the natural 12C and 13C isotopes of carbon in the feed and resultant faeces of animals was studied to develop a technique for estimating the proportion of C3 species (tropical legumes) and C4 species (tropical grasses) selected by grazing animals.

In general, theδ13C values (see text for definition) of faeces from rabbits, sheep, goats and cattle were lower (more negative) than those of the corresponding feeds by from 0·4 to 2·0. This was possibly due to contamination in the gut by tissues or fluids with lower δ13C values. When C4 and C3 feeds were alternated, cattle took about a week to fully achieve the new level (δ13C of – 28·7 on the C3 feed and – 13·1 on the C4 feed) in the faeces. This time lag is associated with the time taken for the feed to move through the digestive tract.

When mixed C3 and C4 feeds were fed to rabbits, sheep, goats and cattle there was a negative linear relation between percentage legume (C3) in the feed and the δ13C of the faeces (P < 0·01). A decrease in one unit in the δ13C value was associated with an increase of 7·0–8·5% legume in the diet.

Estimation of the percentage legume in the feed from the δ13C value of the faeces and of the C3 and C4 components of the diet, resulted in a consistent over estimation of the legume component because the faeces had lower values than the corresponding feeds. This bias was removed if the prediction was based on the δ13C of the feeds minus 1 unit; the legume percentage in the diets of the sheep, goats and cattle could then be estimated with a precision of about ± 5%.

Differences in digestibility between the C3 and C4 components greatly bias the estimations. This bias in the diets fed to rabbits was effectively removed by using in vitro organic matter digestibility values of the two components to correct for the differences. Legume percentage in the diet could then be estimated with a RSD of ± 3%.

Advantages and disadvantages compared with alternative methods of estimating the diet of grazing animals are discussed.

The extents and sites of digestion of organic matter (OM), and its constituent watersoluble carbohydrates, organic acids, pectin, cellulose, hemicellulose and crude protein have been studied in sheep prepared with re-entrant duodenal cannulas and fed four fresh herbage diets, Ruanui perennial ryegrass, Tama Westerwolds ryegrass, Pitau white clover and Fakir sainfoin, at each of two levels of intake.

The water-soluble carbohydrate, organic acids and pectin of all diets were almost completely digested within the rumen. Some 10% of water soluble carbohydrate reached the duodenum on each diet, though this may not have been of dietary origin. Only on legume diets, where pectin concentration was higher, did measurable amounts of pectin reach the intestine, accounting for some 5% of the pectin.

Hemicellulose and cellulose digestibilities differed between diets, being lowest for sainfoin, and next lowest for clover. Between 79 and 94% of digestible hemicellulose was digested in the stomach, but diet and intake had no significant effect on this partition. Of the digestible cellulose, 87–97% was digested in the stomach.

Digestibility of N was lowest for sainfoin and highest for Tama ryegrass. There were no significant differences between herbage species or intake in the percentage of digested N digested in the stomach or intestines. The tannin contained in sainfoin had no effect on nitrogen digestion.

Data from this and other studies reported in the literature were examined as a basis for establishing prediction equations whereby the partition of digestion of the major carbohydrate and nitrogenous constituents in stomach and intestines might be estimated from data obtainable from standard digestibility trials. Regressions were developed for predicting the amounts of OM, cellulose, and hemicellulose digested in the stomach. There are not yet enough suitable data available to predict the amount of nitrogen entering the small intestine.

Numerous dwarf bean accessions were screened for resistance to three strains of bean common mosaic virus (BCMV). Many lines were resistant to a strain of BCMV isolated at Wellesbourne (NVRS) and the Dutch NL4 strain, but only a few lines showed resistance or tolerance to the Dutch NL3 strain. The NVRS strain was found to belong to BCMV Group IVa.

Hybridization experiments showed that resistance to the NVRS strain of BCMV in the dry bean cvs Seafarer and Aurora was controlled by a dominant gene and that in Seafarer this was probably the dominant I gene originally found in Corbett Refugee.

The effects of food restriction on the growth and distribution of bone and on the relation between changes in long bone lengths and changes in limb muscle proportions were studied in 32 Duroc Jersey barrows. Sixteen pigs were fed ad libitum (H group) whilst the other 16 received the same diet on a restricted scale related to live weight.

Animals in each group were slaughtered at times such that the weights of bone in their half carcasses were spread evenly over the range 1·5–4·O kg. The right half carcasses were completely dissected using strictly anatomical criteria.

The results on the relative growth of bone were examined by covariance analysis using the allometric equation.

After adjusting for equal weight of total bone in the side L pigs had heavier femur, tibia-fibula, humerus and radius-ulna and lighter scapula and ribs than H pigs.

Relative to their weights all appendicular long bones were longer in L pigs than in H ones, while there was no such effect on spinal column length.

The effects of the treatment on fore limb muscle proportions relative to total muscle were significantly correlated (P < 0·01) with the changes observed in the lengths of the long bones forming their osseus bases. However, in the case of the hind limb the regression and correlation coefficients were not significantly different from zero.

In summer 1977 a random survey was made of 2250 fields on 1153 farms selected throughout the United Kingdom. Wild oat, Avena spp., was surveyed in all countries; black grass, Alopecurus myosuroides, was surveyed in England and Wales; and couch grass, including Agropyron repens and other perennial grasses, in Scotland and N. Ireland.

Wild oat was reported by farmers on 95% of farms in England, 34% in Wales, 65% in Scotland and 30% in N. Ireland; the areas of infestation in the different countries were 67, 13, 37 and 16% respectively. The majority of wild oat was A.fatua. Only 6% of the cereal area of U.K., including sprayed and unsprayed fields, contained more than one wild oat seed head/m2 (10000/ha), the majority had less than one/20 m2. Black grass was reported on 50% of farms in England (22% of cereal area) mainly in East and South, and on 2% of farms in Wales. Couch grass occurred on 92% of farms in Scotland and 68% in N. Ireland: areas of infestation were 88 and 67% respectively. Most of the infestations of all three weeds had been present for longer than 5 years.

Most farmers intended to eliminate or reduce wild oat and few proposed to hold the weed at its present level or do nothing. Herbicides were used against wild oat on approximately half of the infested area in England and Wales, with proportionately more use in Wales and much less in Scotland and N. Ireland. A third of the black grass infested area of England was treated with a herbicide. There was little spraying against couch grass in Scotland and N. Ireland. Details of dose, time of application and mixing of chemicals were obtained. Wild oat was subsequently found on most of the area treated against this weed, similar observations were made of black grass and couch grass. Most farmers considered herbicide performance good or excellent and those in East and South England believed wild oat to be decreasing as a problem; farmers elsewhere thought the problem to be increasing.

Hand pulling of wild oat (roguing) had occurred on only one tenth of the infested area but a greater area was intended to be rogued after the survey visit. Much of the land that had been rogued was found subsequently to contain few wild oats.

The survey provided information on associations between weed presence, soil type and cropping system, the types of herbicide used and farmers’ impressions of their performance. Comparisons are made with previous surveys in 1972, and information on the disposal of the 1976 crop of straw and on types of cultivation used in different regions is provided. The implications of the results are discussed.

In 16 experiments with field beans at Rothamsted, Woburn and Saxmundham between 1969 and 1976, seed-bed applications to the soil of dieldrin or γ-HCH were used to control subsequent infestations of the roots by larvae of Sitona lineatus. Rates of between 1·12 and 4·48 kg a.i./ha were used. Larval populations on untreated plots plots were variable, but 70–80% control was usually given by rates of 2·24–4·48 kg a.i./ha. Insecticides nearly always increased yields, the mean increase for all treatments being 0·15 t/ha, but a maximum yield response of over 0·5t/ha was achieved. It is suggested that the importance of S. lineatua larvae as pests of field beans in Britain has been under-rated.

A combination of a mineral balance and a radioisotope technique has been used to study the effect of increased intakes of dietary calcium and phosphorus on the Ca and P metabolism of mature, Ca-replete wether sheep. Between Ca intakes of 40 and 100 mg/ day per kg body weight Ca absorption remained constant at a level just sufficient to supply maintenance requirements. Above 100 mg/day per kg body weight, however, absorption increased in direct relation to intake. It is suggested that the increased absorption occurred by diffusion and that at lower Ca intakes, increased diffusion was offset by a corresponding decrease, until it reached a negligible level, in the rate of active absorption.

In spite of the fact that the wethers were already Ca-replete, the increased Ca absorption resulted in increased Ca retention and not as might have been expected in increased excretion. Increased retention was brought about by a decrease in the rate of bone resorption and bone accretion remained constant. Maximum retention occurred when bone resorption ceased and it was equal to the rate of bone accretion. It was only when retention of Ca reached a maximum that further increases in absorption resulted in increased excretion of Ca into urine and intestine. P retention was also increased with increased Ca and P intakes and probably occurred as a result of the increased Ca retention.

The relevence of these findings to the control of parturient paresis (milk fever) in the dairy cow by dietary manipulation is discussed.

Three experiments were carried out to study the effect of replacing milk carbohydrates and part of the milk fat in milk with partially hydrolysed starch (Protamyl 110). Male and female cross-bred lambs (Suffolk × (Finnish Landrace × Dorset Horn)) were used in these experiments. They were weaned from their dams after having received colostrum at 1–2 days of age. The experimental diets were given at room temperature, in eight aliquots, at 3-h intervals through an automated feeding unit. The level of feeding was 1·05 MJ/kg0·75 live weight/day.

In the first experiment, the diets were formulated to contain 28, 17 and 55% of their gross energy as protein, carbohydrate and fat respectively. Diet 1 contained glucose, while diets 2, 3 and 4 had 33, 67 and 100% of glucose respectively replaced by Protamyl. There were no significant differences in growth rate and food utilization between levels of starch inclusion.

In Expt 2, the maximum Protamyl that could be incorporated in lamb milk replacers was examined. Four experimental diets were prepared so that 17 and 55; 25 and 47; 33 and 39; and 41 and 31% of their gross energy was supplied by Protamyl or butter fat respectively. It was found that up to 33% of the gross energy of the diet (41% of the dry matter) could be replaced with Protamyl without adverse effects on lamb performance. When the level of inclusions was increased to 41% of the gross energy (49% of the dry matter), lamb performance was depressed, particularly during the first 15 days of the experiment.

In Expt 3, a direct comparison was made between Protamyl and lactose. The two diets used were similar in composition to diets 1 and 4 in Expt 1, except that lactose was used as a control instead of glucose. There were no differences in growth rate or food utilization as a result of replacing lactose with Protamyl.

The results are discussed in relation to the development of carbohydrases in new born ruminants.

In three experiments the effects of amount and source of nitrogen and energy supplements, and their frequency of feeding, on the voluntary intake and digestion of winter-quality freeze-stored heather (digestibility of organic matter 45%, N content 1·3%) by Scottish Blackface castrated male sheep were examined. The continuous infusion of 0·5gN/day as urea or casein increased voluntary intake by 29% and digestibility of organic matter by 11 percentage units but higher amounts of N supplement gave no further responses. The continuous infusion of a supplement containing 100 g sucrose/day and 3 g N/day as urea gave similar responses in voluntary intake and digestibility of heather to those obtained when N alone was infused. A reduction in the frequency of feeding of the sucrose: urea supplement reduced the response in intake of digestible OM of heather but intakes of digestible OM were higher when an isocaloric supplement of starch: urea was given at the same frequencies (thrice and once daily). The results are discussed in relation to the use of ruminal NH3 concentrations to assess the responses in voluntary intake to N supplementation and the balance required between the nitrogen and energy in the supplement. I t is concluded that the nitrogen and energy supplements could improve the nutrition of sheep grazing heather moorland in winter.

Twelve 6–8 months old male Barbados Blackbelly lambs were used in a 4 × 4 latin square experiment with three replicates to study the utilization of diets made from local by-products and containing 64, 93, 125 or 143 g crude protein/kg D. M.

Both dry-matter (mean 750·1 g/day) and digestible-energy (mean 6·2 MJ DE/day) intakes, and their digestibility coefficients increased, though not significantly, with increasing dietary protein concentration. However, nitrogen digestibility, urinary-nitrogen output and nitrogen retention all increased significantly (P < 0·01) with increasing dietary protein concentration.

Metabolic faecal nitrogen and endogenous urinary nitrogen derived from the intercept of significant regressions of nitrogen intake against urine and faecal nitrogen outputs were 5·07 g/kg dry matter eaten and 3·46 g/day (0·35 kg W0·75) respectively. The diets had a mean biological value of 73·6%. The digestible crude protein requirements for maintenance were (g/day) 29·0, 38·4 and 26·6 when estimated from nitrogen retention, factorially and from live-weight performance respectively.

Twenty-four lactating Jersey cows, grazing a 3-week regrowth of nitrogen-fertilized Chloris gayana cv. Pioneer pastures selected a diet containing 18% crude protein and were given 0, 2 or 4 kg/day of fresh Leucaena leucocephala or 250 g/day of formal-casein. The effect of the treatments on milk production was measured in a 4 × 4 latin-square design experiment with experimental periods of 14 days.

Mean milk yield of unsupplemented cows was 9·6 kg/day, 10·1 kg/day when cows were supplemented with formal-casein and 10·3 kg/day when fed 2 or 4 kg Leucaena/day. Yields of solids-not-fat, protein, casein, butterfat and short and medium-chain (C4–C16) fatty acids in milk fat were higher when cows were fed supplements (P < 0·01). Intake of digestible organic matter was lowest on the unsupplemented diets although feed in excess of 40 kg D.M./cow/day was offered and cows had little difficulty harvesting feed with a mean bite size of 350 mg organic matter/bite and mean grazing time of 507 min/24 h.

It was concluded that a tropical grass diet containing 18% crude protein was deficient in protein for lactating cows and that small quantities of the legume Leucaena can alleviate such a deficiency.